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timcsi 11-09-2009 03:05 PM

Bedroom ceiling corner water stain
Bedroom ceiling corner has water stain. Size of stain looks like 1/4 slice of a large pizza radiating from the corner of the house.

Stain only appears early in the morning as it's cold outside. And as the sun warms the stain is "dried up" in two hours. I noticed that if we turn on central heat overnight the stain appears earlier and then dries up as the sun rises.

What's happening ? I got up to the attic but could not squeeze myself into the corner deep enough to examine it further since I have a low roof. There's no A/C or any venting to the attic so it's dry up there. It has not rained for a while so the outside of the roof is dry and there's no visible opening of the soffit to the outside. The corner of the wall is far away from the bathroom.

Am I dealing with some issue of condensation building up in the ceiling drywall ? How to check and diagnose this ?

Is it recommended that I remove some shingles from that corner of the roof in order to see if there's a hole/opening to the roof sheelding ? How to proper remove existing shingles and re-seal the spot with new shingles ?

stuart45 11-09-2009 03:54 PM

It does sound like condensation. We get it every morning on our single glazed windows, even with the window left open.
My wife and a J cloth is the answer.
You do give off a lot of moisture at night and it will condense on the coldest spots.
The way that a surveyor tests for condensation is to take the air temperature and R/H of the room, and the surface temperature of the elements like walls and ceilings where the moisture is said to be forming.

timcsi 11-09-2009 04:08 PM

so this is just surface condensation on the ceiling wall ? If so that's OK because I'm worried about frost forming and melting on the attic that seeps through the wood and get to the ceiling drywall. How do I check ?

stuart45 11-10-2009 04:07 PM

You could tape a piece of polythene tight to the ceiling and see if the moisture forms on top or underneath.

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